Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints

[Paul E. McKenney]

On Wed, Jun 24, 2015 at 01:14:18PM -0700, Stephen Boyd wrote:
> John Stultz reported an RCU splat on ARM with ipi trace events
> enabled. It looks like the same problem exists on ARM64.
> 
> At this point in the IPI handling path we haven't called
> irq_enter() yet, so RCU doesn't know that we're about to exit
> idle and properly warns that we're using RCU from an idle CPU.
> Use trace_ipi_entry_rcuidle() instead of trace_ipi_entry() so
> that RCU is informed about our exit from idle.
> 
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
> Fixes: 45ed695ac10a "ARM64: add IPI tracepoints"
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>

Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

> ---
> 
> I haven't confirmed this, but it looks an awful lot like the same
> problem exists on ARM64.
> 
>  arch/arm64/kernel/smp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 4b2121bd7f9c..a1883bfdd9d6 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -693,7 +693,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>  	struct pt_regs *old_regs = set_irq_regs(regs);
> 
>  	if ((unsigned)ipinr < NR_IPI) {
> -		trace_ipi_entry(ipi_types[ipinr]);
> +		trace_ipi_entry_rcuidle(ipi_types[ipinr]);
>  		__inc_irq_stat(cpu, ipi_irqs[ipinr]);
>  	}
> 
> @@ -736,7 +736,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>  	}
> 
>  	if ((unsigned)ipinr < NR_IPI)
> -		trace_ipi_exit(ipi_types[ipinr]);
> +		trace_ipi_exit_rcuidle(ipi_types[ipinr]);
>  	set_irq_regs(old_regs);
>  }
> 
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 

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